The balloon - big enough to fill the Rose Bowl football stadium in Pasadena, California - lifted off at 2:40 p.m. EDT (1840 GMT) for what was expected to be a three-hour climb to 120,000 feet (36,576 meters) above the Pacific Ocean.

The launch, which was delayed six times this month because of unsuitable weather, and the test were broadcast live on NASA Television.

Once in position, the saucer-shaped Low Density Supersonic Decelerator, or LDSD, craft will be released from the balloon so its rocket motor can fire to blast the vehicle up to 180,000 feet (54,900 meters).

Next, a doughnut-shaped shield was to inflate, slowing the vehicle from about 3,000 mph (4,828 kph) - roughly four times the speed of sound - to about half that speed.

Finally, a massive, 110-foot (34-meter) diameter parachute was to deploy to carry the vehicle to controlled splashdown in the ocean.

"It's the largest supersonic parachute that we've ever tested - over twice the area of the parachute that we used to land Curiosity (rover) on Mars a couple of years ago," said NASA engineer Dan Coatta, with the Jet Propulsion Laboratory in Pasadena, California.

The point of the test is to put a prototype landing system through conditions that would be experienced on Mars.

"When we're actually going to use it for real, it's going to be on a spacecraft, entering the atmosphere of Mars at thousands of miles per hour, so we have to come up with some way on Earth to simulate that condition in order to prove that these things work," Coatta said during commentary as the balloon was prepared for launch.

The test is part of a larger technology-developing initiative to prepare to send heavier rovers and eventually human habitats to Mars.